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<meta name="description" content="C# 多态性   多态是同一个行为具有多个不同表现形式或形态的能力。 多态性意味着有多重形式。在面向对象编程范式中，多态性往往表现为“一个接口，多个功能”。 多态性可以是静态的或动态的。在静态多态性中，函数的响应是在编译时发生的。在动态多态性中，函数的响应是在运行时发生的。 在 C# 中，每个类型都是多态的，因为包括用户定义类型在内的所有类型都继承自 Object。  多态就是同一个接口，使用不同的实例而执行不同操作，如图所示：    ..">
		
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			<h1>C# <span class="color_h1">多态性</span></h1>


<p>多态是同一个行为具有多个不同表现形式或形态的能力。</p>
<p><b>多态性</b>意味着有多重形式。在面向对象编程范式中，多态性往往表现为"一个接口，多个功能"。</p>
<p>多态性可以是静态的或动态的。在<b>静态多态性</b>中，函数的响应是在编译时发生的。在<b>动态多态性</b>中，函数的响应是在运行时发生的。</p>
<p>在 C# 中，每个类型都是多态的，因为包括用户定义类型在内的所有类型都继承自 Object。</p>

<p>多态就是同一个接口，使用不同的实例而执行不同操作，如图所示：</p>
<p><img decoding="async" src="//www.runoob.com/wp-content/uploads/2013/12/dt-java.png"></p>

<blockquote>
<p>现实中，比如我们按下 F1 键这个动作：
</p>
<ul><li>
如果当前在 Flash 界面下弹出的就是 AS 3 的帮助文档；</li><li>如果当前在 Word 下弹出的就是 Word 帮助；</li><li>在 Windows 下弹出的就是 Windows 帮助和支持。</li></ul><p>同一个事件发生在不同的对象上会产生不同的结果。</p>
</blockquote>
<h2 class="tutheader">静态多态性</h2>
<p>在编译时，函数和对象的连接机制被称为早期绑定，也被称为静态绑定。C# 提供了两种技术来实现静态多态性。分别为：</p>
<ul class="list">
<li>函数重载</li>
<li>运算符重载</li>
</ul>
<p>运算符重载将在下一章节讨论，接下来我们将讨论函数重载。</p>
<hr>
<h2 id="overload">函数重载</h2>
<p>您可以在同一个范围内对相同的函数名有多个定义。函数的定义必须彼此不同，可以是参数列表中的参数类型不同，也可以是参数个数不同。不能重载只有返回类型不同的函数声明。</p>

<p>下面的实例演示了几个相同的函数 <b>Add()</b>，用于对不同个数参数进行相加处理：</p>
<div class="example"><h2 class="example">实例</h2> <div class="example_code">
<span style="color: #05a; font-weight: bold;">using</span> <span style="color: #696969;">System</span><span style="color: #008000;">;</span><br />
<span style="color: #05a; font-weight: bold;">namespace</span> PolymorphismApplication<br />
<span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp; <span style="color: #05a; font-weight: bold;">public</span> <span style="color: #6666cc; font-weight: bold;">class</span> TestData &nbsp;<br />
&nbsp; &nbsp; <span style="color: #008000;">&#123;</span> &nbsp;<br />
&nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #05a; font-weight: bold;">public</span> <span style="color: #6666cc; font-weight: bold;">int</span> <span style="color: #05a; font-weight: bold;">Add</span><span style="color: #008000;">&#40;</span><span style="color: #6666cc; font-weight: bold;">int</span> a, <span style="color: #6666cc; font-weight: bold;">int</span> b, <span style="color: #6666cc; font-weight: bold;">int</span> c<span style="color: #008000;">&#41;</span> &nbsp;<br />
&nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#123;</span> &nbsp;<br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #05a; font-weight: bold;">return</span> a <span style="color: #008000;">+</span> b <span style="color: #008000;">+</span> c<span style="color: #008000;">;</span> &nbsp;<br />
&nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#125;</span> &nbsp;<br />
&nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #05a; font-weight: bold;">public</span> <span style="color: #6666cc; font-weight: bold;">int</span> <span style="color: #05a; font-weight: bold;">Add</span><span style="color: #008000;">&#40;</span><span style="color: #6666cc; font-weight: bold;">int</span> a, <span style="color: #6666cc; font-weight: bold;">int</span> b<span style="color: #008000;">&#41;</span> &nbsp;<br />
&nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#123;</span> &nbsp;<br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #05a; font-weight: bold;">return</span> a <span style="color: #008000;">+</span> b<span style="color: #008000;">;</span> &nbsp;<br />
&nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#125;</span> &nbsp;<br />
&nbsp; &nbsp; <span style="color: #008000;">&#125;</span> &nbsp;<br />
&nbsp; &nbsp; <span style="color: #6666cc; font-weight: bold;">class</span> Program &nbsp;<br />
&nbsp; &nbsp; <span style="color: #008000;">&#123;</span> &nbsp;<br />
&nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #05a; font-weight: bold;">static</span> <span style="color: #6666cc; font-weight: bold;">void</span> Main<span style="color: #008000;">&#40;</span><span style="color: #6666cc; font-weight: bold;">string</span><span style="color: #008000;">&#91;</span><span style="color: #008000;">&#93;</span> args<span style="color: #008000;">&#41;</span> &nbsp;<br />
&nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#123;</span> &nbsp;<br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; TestData dataClass <span style="color: #008000;">=</span> <span style="color: #008000;">new</span> TestData<span style="color: #008000;">&#40;</span><span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #6666cc; font-weight: bold;">int</span> add1 <span style="color: #008000;">=</span> dataClass<span style="color: #008000;">.</span><span style="color: #05a; font-weight: bold;">Add</span><span style="color: #008000;">&#40;</span><span style="color: Maroon;">1</span>, <span style="color: Maroon;">2</span><span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span> &nbsp;<br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #6666cc; font-weight: bold;">int</span> add2 <span style="color: #008000;">=</span> dataClass<span style="color: #008000;">.</span><span style="color: #05a; font-weight: bold;">Add</span><span style="color: #008000;">&#40;</span><span style="color: Maroon;">1</span>, <span style="color: Maroon;">2</span>, <span style="color: Maroon;">3</span><span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
<br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Console<span style="color: #008000;">.</span><span style="color: #05a;">WriteLine</span><span style="color: #008000;">&#40;</span><span style="color: #a11;">&quot;add1 :&quot;</span> <span style="color: #008000;">+</span> add1<span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Console<span style="color: #008000;">.</span><span style="color: #05a;">WriteLine</span><span style="color: #008000;">&#40;</span><span style="color: #a11;">&quot;add2 :&quot;</span> <span style="color: #008000;">+</span> add2<span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span> &nbsp;<br />
&nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#125;</span> &nbsp;<br />
&nbsp; &nbsp; <span style="color: #008000;">&#125;</span> &nbsp;<br />
<span style="color: #008000;">&#125;</span><br />
</div></div>

<p>下面的实例演示了几个相同的函数 <b>print()</b>，用于打印不同的数据类型：</p>

<div class="example"><h2 class="example">实例</h2><div class="example_code">
<span style="color: #05a; font-weight: bold;">using</span> <span style="color: #696969;">System</span><span style="color: #008000;">;</span><br />
<span style="color: #05a; font-weight: bold;">namespace</span> PolymorphismApplication<br />
<span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp;<span style="color: #6666cc; font-weight: bold;">class</span> Printdata<br />
&nbsp; &nbsp;<span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #6666cc; font-weight: bold;">void</span> print<span style="color: #008000;">&#40;</span><span style="color: #6666cc; font-weight: bold;">int</span> i<span style="color: #008000;">&#41;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Console<span style="color: #008000;">.</span><span style="color: #05a;">WriteLine</span><span style="color: #008000;">&#40;</span><span style="color: #a11;">&quot;输出整型: {0}&quot;</span>, i <span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#125;</span><br />
<br />
&nbsp; &nbsp; &nbsp; <span style="color: #6666cc; font-weight: bold;">void</span> print<span style="color: #008000;">&#40;</span><span style="color: #6666cc; font-weight: bold;">double</span> f<span style="color: #008000;">&#41;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Console<span style="color: #008000;">.</span><span style="color: #05a;">WriteLine</span><span style="color: #008000;">&#40;</span><span style="color: #a11;">&quot;输出浮点型: {0}&quot;</span> , f<span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#125;</span><br />
<br />
&nbsp; &nbsp; &nbsp; <span style="color: #6666cc; font-weight: bold;">void</span> print<span style="color: #008000;">&#40;</span><span style="color: #6666cc; font-weight: bold;">string</span> s<span style="color: #008000;">&#41;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Console<span style="color: #008000;">.</span><span style="color: #05a;">WriteLine</span><span style="color: #008000;">&#40;</span><span style="color: #a11;">&quot;输出字符串: {0}&quot;</span>, s<span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#125;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #05a; font-weight: bold;">static</span> <span style="color: #6666cc; font-weight: bold;">void</span> Main<span style="color: #008000;">&#40;</span><span style="color: #6666cc; font-weight: bold;">string</span><span style="color: #008000;">&#91;</span><span style="color: #008000;">&#93;</span> args<span style="color: #008000;">&#41;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Printdata p <span style="color: #008000;">=</span> <span style="color: #008000;">new</span> Printdata<span style="color: #008000;">&#40;</span><span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<span style="color: #696969; font-style: italic;">// 调用 print 来打印整数</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;p<span style="color: #008000;">.</span><span style="color: #05a;">print</span><span style="color: #008000;">&#40;</span><span style="color: Maroon;">1</span><span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<span style="color: #696969; font-style: italic;">// 调用 print 来打印浮点数</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;p<span style="color: #008000;">.</span><span style="color: #05a;">print</span><span style="color: #008000;">&#40;</span><span style="color: Maroon;">1.23</span><span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<span style="color: #696969; font-style: italic;">// 调用 print 来打印字符串</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;p<span style="color: #008000;">.</span><span style="color: #05a;">print</span><span style="color: #008000;">&#40;</span><span style="color: #a11;">&quot;Hello Runoob&quot;</span><span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Console<span style="color: #008000;">.</span><span style="color: #05a;">ReadKey</span><span style="color: #008000;">&#40;</span><span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#125;</span><br />
&nbsp; &nbsp;<span style="color: #008000;">&#125;</span><br />
<span style="color: #008000;">&#125;</span><br />
<br />
</div></div>

<p>当上面的代码被编译和执行时，它会产生下列结果：</p>
<pre>
输出整型: 1
输出浮点型: 1.23
输出字符串: Hello Runoob
</pre>
<hr>
<h2 id="override">动态多态性</h2>
<p>C# 允许您使用关键字 <b>abstract</b> 创建抽象类，用于提供接口的部分类的实现。当一个派生类继承自该抽象类时，实现即完成。<b>抽象类</b>包含抽象方法，抽象方法可被派生类实现。派生类具有更专业的功能。</p>
<p>请注意，下面是有关抽象类的一些规则：</p>
<ul class="list">
<li>您不能创建一个抽象类的实例。</li>
<li>您不能在一个抽象类外部声明一个抽象方法。</li>
<li>通过在类定义前面放置关键字 <b>sealed</b>，可以将类声明为<b>密封类</b>。当一个类被声明为 <b>sealed</b> 时，它不能被继承。抽象类不能被声明为 sealed。</li>
</ul>
<p>下面的程序演示了一个抽象类：</p>
<div class="example"><h2 class="example">实例</h2><div class="example_code">
<span style="color: #05a; font-weight: bold;">using</span> <span style="color: #696969;">System</span><span style="color: #008000;">;</span><br />
<span style="color: #05a; font-weight: bold;">namespace</span> PolymorphismApplication<br />
<span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp;<span style="color: #05a; font-weight: bold;">abstract</span> <span style="color: #6666cc; font-weight: bold;">class</span> Shape<br />
&nbsp; &nbsp;<span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp;<span style="color: #05a; font-weight: bold;">abstract</span> <span style="color: #05a; font-weight: bold;">public</span> <span style="color: #6666cc; font-weight: bold;">int</span> area<span style="color: #008000;">&#40;</span><span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp;<span style="color: #008000;">&#125;</span><br />
&nbsp; &nbsp;<span style="color: #6666cc; font-weight: bold;">class</span> Rectangle<span style="color: #008000;">:</span> &nbsp;Shape<br />
&nbsp; &nbsp;<span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #05a; font-weight: bold;">private</span> <span style="color: #6666cc; font-weight: bold;">int</span> length<span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #05a; font-weight: bold;">private</span> <span style="color: #6666cc; font-weight: bold;">int</span> width<span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #05a; font-weight: bold;">public</span> Rectangle<span style="color: #008000;">&#40;</span> <span style="color: #6666cc; font-weight: bold;">int</span> a<span style="color: #008000;">=</span><span style="color: Maroon;">0</span>, <span style="color: #6666cc; font-weight: bold;">int</span> b<span style="color: #008000;">=</span><span style="color: Maroon;">0</span><span style="color: #008000;">&#41;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;length <span style="color: #008000;">=</span> a<span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;width <span style="color: #008000;">=</span> b<span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#125;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #05a; font-weight: bold;">public</span> <span style="color: #05a; font-weight: bold;">override</span> <span style="color: #6666cc; font-weight: bold;">int</span> area <span style="color: #008000;">&#40;</span><span style="color: #008000;">&#41;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#123;</span> <br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Console<span style="color: #008000;">.</span><span style="color: #05a;">WriteLine</span><span style="color: #008000;">&#40;</span><span style="color: #a11;">&quot;Rectangle 类的面积：&quot;</span><span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<span style="color: #05a; font-weight: bold;">return</span> <span style="color: #008000;">&#40;</span>width <span style="color: #008000;">*</span> length<span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span> <br />
&nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#125;</span><br />
&nbsp; &nbsp;<span style="color: #008000;">&#125;</span><br />
<br />
&nbsp; &nbsp;<span style="color: #6666cc; font-weight: bold;">class</span> RectangleTester<br />
&nbsp; &nbsp;<span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #05a; font-weight: bold;">static</span> <span style="color: #6666cc; font-weight: bold;">void</span> Main<span style="color: #008000;">&#40;</span><span style="color: #6666cc; font-weight: bold;">string</span><span style="color: #008000;">&#91;</span><span style="color: #008000;">&#93;</span> args<span style="color: #008000;">&#41;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Rectangle r <span style="color: #008000;">=</span> <span style="color: #008000;">new</span> Rectangle<span style="color: #008000;">&#40;</span><span style="color: Maroon;">10</span>, <span style="color: Maroon;">7</span><span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<span style="color: #6666cc; font-weight: bold;">double</span> a <span style="color: #008000;">=</span> r<span style="color: #008000;">.</span><span style="color: #05a;">area</span><span style="color: #008000;">&#40;</span><span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Console<span style="color: #008000;">.</span><span style="color: #05a;">WriteLine</span><span style="color: #008000;">&#40;</span><span style="color: #a11;">&quot;面积： {0}&quot;</span>,a<span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Console<span style="color: #008000;">.</span><span style="color: #05a;">ReadKey</span><span style="color: #008000;">&#40;</span><span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#125;</span><br />
&nbsp; &nbsp;<span style="color: #008000;">&#125;</span><br />
<span style="color: #008000;">&#125;</span><br />
</div></div>
<p>当上面的代码被编译和执行时，它会产生下列结果：</p>
<pre>
Rectangle 类的面积：
面积： 70
</pre>
<p>当有一个定义在类中的函数需要在继承类中实现时，可以使用<b>虚方法</b>。</p><p>虚方法是使用关键字 <b>virtual</b> 声明的。

</p><p>虚方法可以在不同的继承类中有不同的实现。</p><p>对虚方法的调用是在运行时发生的。</p>
<p>动态多态性是通过 <b>抽象类</b> 和 <b>虚方法</b> 实现的。</p>



<p>
以下实例创建了 Shape 基类，并创建派生类 Circle、 Rectangle、Triangle， Shape 类提供一个名为 Draw 的虚拟方法，在每个派生类中重写该方法以绘制该类的指定形状。</p>

<div class="example"><h2 class="example">实例</h2> <div class="example_code">
<span style="color: #05a; font-weight: bold;">using</span> <span style="color: #696969;">System</span><span style="color: #008000;">;</span><br />
<span style="color: #05a; font-weight: bold;">using</span> <span style="color: #696969;">System.Collections.Generic</span><span style="color: #008000;">;</span><br />
<br />
<span style="color: #05a; font-weight: bold;">public</span> <span style="color: #6666cc; font-weight: bold;">class</span> Shape<br />
<span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp; <span style="color: #05a; font-weight: bold;">public</span> <span style="color: #6666cc; font-weight: bold;">int</span> X <span style="color: #008000;">&#123;</span> <span style="color: #05a; font-weight: bold;">get</span><span style="color: #008000;">;</span> <span style="color: #05a; font-weight: bold;">private</span> <span style="color: #05a; font-weight: bold;">set</span><span style="color: #008000;">;</span> <span style="color: #008000;">&#125;</span><br />
&nbsp; &nbsp; <span style="color: #05a; font-weight: bold;">public</span> <span style="color: #6666cc; font-weight: bold;">int</span> Y <span style="color: #008000;">&#123;</span> <span style="color: #05a; font-weight: bold;">get</span><span style="color: #008000;">;</span> <span style="color: #05a; font-weight: bold;">private</span> <span style="color: #05a; font-weight: bold;">set</span><span style="color: #008000;">;</span> <span style="color: #008000;">&#125;</span><br />
&nbsp; &nbsp; <span style="color: #05a; font-weight: bold;">public</span> <span style="color: #6666cc; font-weight: bold;">int</span> Height <span style="color: #008000;">&#123;</span> <span style="color: #05a; font-weight: bold;">get</span><span style="color: #008000;">;</span> <span style="color: #05a; font-weight: bold;">set</span><span style="color: #008000;">;</span> <span style="color: #008000;">&#125;</span><br />
&nbsp; &nbsp; <span style="color: #05a; font-weight: bold;">public</span> <span style="color: #6666cc; font-weight: bold;">int</span> Width <span style="color: #008000;">&#123;</span> <span style="color: #05a; font-weight: bold;">get</span><span style="color: #008000;">;</span> <span style="color: #05a; font-weight: bold;">set</span><span style="color: #008000;">;</span> <span style="color: #008000;">&#125;</span><br />
&nbsp; &nbsp;<br />
&nbsp; &nbsp; <span style="color: #696969; font-style: italic;">// 虚方法</span><br />
&nbsp; &nbsp; <span style="color: #05a; font-weight: bold;">public</span> <span style="color: #05a; font-weight: bold;">virtual</span> <span style="color: #6666cc; font-weight: bold;">void</span> Draw<span style="color: #008000;">&#40;</span><span style="color: #008000;">&#41;</span><br />
&nbsp; &nbsp; <span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; Console<span style="color: #008000;">.</span><span style="color: #05a;">WriteLine</span><span style="color: #008000;">&#40;</span><span style="color: #a11;">&quot;执行基类的画图任务&quot;</span><span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; <span style="color: #008000;">&#125;</span><br />
<span style="color: #008000;">&#125;</span><br />
<br />
<span style="color: #6666cc; font-weight: bold;">class</span> Circle <span style="color: #008000;">:</span> Shape<br />
<span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp; <span style="color: #05a; font-weight: bold;">public</span> <span style="color: #05a; font-weight: bold;">override</span> <span style="color: #6666cc; font-weight: bold;">void</span> Draw<span style="color: #008000;">&#40;</span><span style="color: #008000;">&#41;</span><br />
&nbsp; &nbsp; <span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; Console<span style="color: #008000;">.</span><span style="color: #05a;">WriteLine</span><span style="color: #008000;">&#40;</span><span style="color: #a11;">&quot;画一个圆形&quot;</span><span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #05a; font-weight: bold;">base</span><span style="color: #008000;">.</span><span style="color: #05a;">Draw</span><span style="color: #008000;">&#40;</span><span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; <span style="color: #008000;">&#125;</span><br />
<span style="color: #008000;">&#125;</span><br />
<span style="color: #6666cc; font-weight: bold;">class</span> Rectangle <span style="color: #008000;">:</span> Shape<br />
<span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp; <span style="color: #05a; font-weight: bold;">public</span> <span style="color: #05a; font-weight: bold;">override</span> <span style="color: #6666cc; font-weight: bold;">void</span> Draw<span style="color: #008000;">&#40;</span><span style="color: #008000;">&#41;</span><br />
&nbsp; &nbsp; <span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; Console<span style="color: #008000;">.</span><span style="color: #05a;">WriteLine</span><span style="color: #008000;">&#40;</span><span style="color: #a11;">&quot;画一个长方形&quot;</span><span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #05a; font-weight: bold;">base</span><span style="color: #008000;">.</span><span style="color: #05a;">Draw</span><span style="color: #008000;">&#40;</span><span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; <span style="color: #008000;">&#125;</span><br />
<span style="color: #008000;">&#125;</span><br />
<span style="color: #6666cc; font-weight: bold;">class</span> Triangle <span style="color: #008000;">:</span> Shape<br />
<span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp; <span style="color: #05a; font-weight: bold;">public</span> <span style="color: #05a; font-weight: bold;">override</span> <span style="color: #6666cc; font-weight: bold;">void</span> Draw<span style="color: #008000;">&#40;</span><span style="color: #008000;">&#41;</span><br />
&nbsp; &nbsp; <span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; Console<span style="color: #008000;">.</span><span style="color: #05a;">WriteLine</span><span style="color: #008000;">&#40;</span><span style="color: #a11;">&quot;画一个三角形&quot;</span><span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #05a; font-weight: bold;">base</span><span style="color: #008000;">.</span><span style="color: #05a;">Draw</span><span style="color: #008000;">&#40;</span><span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; <span style="color: #008000;">&#125;</span><br />
<span style="color: #008000;">&#125;</span><br />
<br />
<span style="color: #6666cc; font-weight: bold;">class</span> Program<br />
<span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp; <span style="color: #05a; font-weight: bold;">static</span> <span style="color: #6666cc; font-weight: bold;">void</span> Main<span style="color: #008000;">&#40;</span><span style="color: #6666cc; font-weight: bold;">string</span><span style="color: #008000;">&#91;</span><span style="color: #008000;">&#93;</span> args<span style="color: #008000;">&#41;</span><br />
&nbsp; &nbsp; <span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #696969; font-style: italic;">// 创建一个 List&lt;Shape&gt; 对象，并向该对象添加 Circle、Triangle 和 Rectangle</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #05a; font-weight: bold;">var</span> shapes <span style="color: #008000;">=</span> <span style="color: #008000;">new</span> List<span style="color: #008000;">&lt;</span>Shape<span style="color: #008000;">&gt;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #008000;">new</span> Rectangle<span style="color: #008000;">&#40;</span><span style="color: #008000;">&#41;</span>,<br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #008000;">new</span> Triangle<span style="color: #008000;">&#40;</span><span style="color: #008000;">&#41;</span>,<br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #008000;">new</span> Circle<span style="color: #008000;">&#40;</span><span style="color: #008000;">&#41;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#125;</span><span style="color: #008000;">;</span><br />
<br />
&nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #696969; font-style: italic;">// 使用 foreach 循环对该列表的派生类进行循环访问，并对其中的每个 Shape 对象调用 Draw 方法 </span><br />
&nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #05a; font-weight: bold;">foreach</span> <span style="color: #008000;">&#40;</span><span style="color: #05a; font-weight: bold;">var</span> shape <span style="color: #05a; font-weight: bold;">in</span> shapes<span style="color: #008000;">&#41;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; shape<span style="color: #008000;">.</span><span style="color: #05a;">Draw</span><span style="color: #008000;">&#40;</span><span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#125;</span><br />
<br />
&nbsp; &nbsp; &nbsp; &nbsp; Console<span style="color: #008000;">.</span><span style="color: #05a;">WriteLine</span><span style="color: #008000;">&#40;</span><span style="color: #a11;">&quot;按下任意键退出。&quot;</span><span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; Console<span style="color: #008000;">.</span><span style="color: #05a;">ReadKey</span><span style="color: #008000;">&#40;</span><span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; <span style="color: #008000;">&#125;</span><br />
<br />
<span style="color: #008000;">&#125;</span><br />
</div></div>
<p>当上面的代码被编译和执行时，它会产生下列结果：</p>
<pre>
画一个长方形
执行基类的画图任务
画一个三角形
执行基类的画图任务
画一个圆形
执行基类的画图任务
按下任意键退出。
</pre>

<p>下面的程序演示通过虚方法 area() 来计算不同形状图像的面积：</p>
<div class="example"><h2 class="example">实例</h2><div class="example_code">
<span style="color: #05a; font-weight: bold;">using</span> <span style="color: #696969;">System</span><span style="color: #008000;">;</span><br />
<span style="color: #05a; font-weight: bold;">namespace</span> PolymorphismApplication<br />
<span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp;<span style="color: #6666cc; font-weight: bold;">class</span> Shape <br />
&nbsp; &nbsp;<span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #05a; font-weight: bold;">protected</span> <span style="color: #6666cc; font-weight: bold;">int</span> width, height<span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #05a; font-weight: bold;">public</span> Shape<span style="color: #008000;">&#40;</span> <span style="color: #6666cc; font-weight: bold;">int</span> a<span style="color: #008000;">=</span><span style="color: Maroon;">0</span>, <span style="color: #6666cc; font-weight: bold;">int</span> b<span style="color: #008000;">=</span><span style="color: Maroon;">0</span><span style="color: #008000;">&#41;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;width <span style="color: #008000;">=</span> a<span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;height <span style="color: #008000;">=</span> b<span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#125;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #05a; font-weight: bold;">public</span> <span style="color: #05a; font-weight: bold;">virtual</span> <span style="color: #6666cc; font-weight: bold;">int</span> area<span style="color: #008000;">&#40;</span><span style="color: #008000;">&#41;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Console<span style="color: #008000;">.</span><span style="color: #05a;">WriteLine</span><span style="color: #008000;">&#40;</span><span style="color: #a11;">&quot;父类的面积：&quot;</span><span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<span style="color: #05a; font-weight: bold;">return</span> <span style="color: Maroon;">0</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#125;</span><br />
&nbsp; &nbsp;<span style="color: #008000;">&#125;</span><br />
&nbsp; &nbsp;<span style="color: #6666cc; font-weight: bold;">class</span> Rectangle<span style="color: #008000;">:</span> Shape<br />
&nbsp; &nbsp;<span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #05a; font-weight: bold;">public</span> Rectangle<span style="color: #008000;">&#40;</span> <span style="color: #6666cc; font-weight: bold;">int</span> a<span style="color: #008000;">=</span><span style="color: Maroon;">0</span>, <span style="color: #6666cc; font-weight: bold;">int</span> b<span style="color: #008000;">=</span><span style="color: Maroon;">0</span><span style="color: #008000;">&#41;</span><span style="color: #008000;">:</span> <span style="color: #05a; font-weight: bold;">base</span><span style="color: #008000;">&#40;</span>a, b<span style="color: #008000;">&#41;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#123;</span><br />
<br />
&nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#125;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #05a; font-weight: bold;">public</span> <span style="color: #05a; font-weight: bold;">override</span> <span style="color: #6666cc; font-weight: bold;">int</span> area <span style="color: #008000;">&#40;</span><span style="color: #008000;">&#41;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Console<span style="color: #008000;">.</span><span style="color: #05a;">WriteLine</span><span style="color: #008000;">&#40;</span><span style="color: #a11;">&quot;Rectangle 类的面积：&quot;</span><span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<span style="color: #05a; font-weight: bold;">return</span> <span style="color: #008000;">&#40;</span>width <span style="color: #008000;">*</span> height<span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span> <br />
&nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#125;</span><br />
&nbsp; &nbsp;<span style="color: #008000;">&#125;</span><br />
&nbsp; &nbsp;<span style="color: #6666cc; font-weight: bold;">class</span> Triangle<span style="color: #008000;">:</span> Shape<br />
&nbsp; &nbsp;<span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #05a; font-weight: bold;">public</span> Triangle<span style="color: #008000;">&#40;</span><span style="color: #6666cc; font-weight: bold;">int</span> a <span style="color: #008000;">=</span> <span style="color: Maroon;">0</span>, <span style="color: #6666cc; font-weight: bold;">int</span> b <span style="color: #008000;">=</span> <span style="color: Maroon;">0</span><span style="color: #008000;">&#41;</span><span style="color: #008000;">:</span> <span style="color: #05a; font-weight: bold;">base</span><span style="color: #008000;">&#40;</span>a, b<span style="color: #008000;">&#41;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp; &nbsp; <br />
&nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#125;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #05a; font-weight: bold;">public</span> <span style="color: #05a; font-weight: bold;">override</span> <span style="color: #6666cc; font-weight: bold;">int</span> area<span style="color: #008000;">&#40;</span><span style="color: #008000;">&#41;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Console<span style="color: #008000;">.</span><span style="color: #05a;">WriteLine</span><span style="color: #008000;">&#40;</span><span style="color: #a11;">&quot;Triangle 类的面积：&quot;</span><span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<span style="color: #05a; font-weight: bold;">return</span> <span style="color: #008000;">&#40;</span>width <span style="color: #008000;">*</span> height <span style="color: #008000;">/</span> <span style="color: Maroon;">2</span><span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span> <br />
&nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#125;</span><br />
&nbsp; &nbsp;<span style="color: #008000;">&#125;</span><br />
&nbsp; &nbsp;<span style="color: #6666cc; font-weight: bold;">class</span> Caller<br />
&nbsp; &nbsp;<span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #05a; font-weight: bold;">public</span> <span style="color: #6666cc; font-weight: bold;">void</span> CallArea<span style="color: #008000;">&#40;</span>Shape sh<span style="color: #008000;">&#41;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<span style="color: #6666cc; font-weight: bold;">int</span> a<span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;a <span style="color: #008000;">=</span> sh<span style="color: #008000;">.</span><span style="color: #05a;">area</span><span style="color: #008000;">&#40;</span><span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Console<span style="color: #008000;">.</span><span style="color: #05a;">WriteLine</span><span style="color: #008000;">&#40;</span><span style="color: #a11;">&quot;面积： {0}&quot;</span>, a<span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#125;</span><br />
&nbsp; &nbsp;<span style="color: #008000;">&#125;</span> &nbsp;<br />
&nbsp; &nbsp;<span style="color: #6666cc; font-weight: bold;">class</span> Tester<br />
&nbsp; &nbsp;<span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp; &nbsp; <br />
&nbsp; &nbsp; &nbsp; <span style="color: #05a; font-weight: bold;">static</span> <span style="color: #6666cc; font-weight: bold;">void</span> Main<span style="color: #008000;">&#40;</span><span style="color: #6666cc; font-weight: bold;">string</span><span style="color: #008000;">&#91;</span><span style="color: #008000;">&#93;</span> args<span style="color: #008000;">&#41;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#123;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Caller c <span style="color: #008000;">=</span> <span style="color: #008000;">new</span> Caller<span style="color: #008000;">&#40;</span><span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Rectangle r <span style="color: #008000;">=</span> <span style="color: #008000;">new</span> Rectangle<span style="color: #008000;">&#40;</span><span style="color: Maroon;">10</span>, <span style="color: Maroon;">7</span><span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Triangle t <span style="color: #008000;">=</span> <span style="color: #008000;">new</span> Triangle<span style="color: #008000;">&#40;</span><span style="color: Maroon;">10</span>, <span style="color: Maroon;">5</span><span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;c<span style="color: #008000;">.</span><span style="color: #05a;">CallArea</span><span style="color: #008000;">&#40;</span>r<span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;c<span style="color: #008000;">.</span><span style="color: #05a;">CallArea</span><span style="color: #008000;">&#40;</span>t<span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Console<span style="color: #008000;">.</span><span style="color: #05a;">ReadKey</span><span style="color: #008000;">&#40;</span><span style="color: #008000;">&#41;</span><span style="color: #008000;">;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #008000;">&#125;</span><br />
&nbsp; &nbsp;<span style="color: #008000;">&#125;</span><br />
<span style="color: #008000;">&#125;</span><br />
</div></div>
<p>当上面的代码被编译和执行时，它会产生下列结果：</p>
<pre>
Rectangle 类的面积：
面积：70
Triangle 类的面积：
面积：25
</pre>			<!-- 其他扩展 -->
						
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<div id="postcomments"  style="display:none;" >
	<ol class="commentlist">
		<li class="comment even thread-even depth-1" id="comment-10267"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;yuri</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;246***6318@qq.com</p></div><div id="runoobvote-id-10267" data-commid = "10267" class="upvotejs"><a class="upvote"></a> <span class="count">65</span></div></div><div class="comt-main" id="div-comment-10267"><h2>C# 多态性</h2>
<p>
<strong>多态：</strong>一个接口多个功能。</p><p>
<strong>静态多态性：</strong>编译时发生函数响应（调用）；</p>
<p><strong>动态多态性：</strong>运行时发生函数响应。</p><p>

<strong>静态绑定（早期绑定）：</strong>编译时函数和对象的连接机制。

两种技术实现静态多态性：函数重载/运算符重载。</p>
<p>
<strong>函数重载：</strong>在同一范围内对相同函数名有多个定义，可以是参数类型或参数个数的不同，但不许只有返回值类型不同。
</p><p>
<strong>运算符重载：</strong></p><p>
关键字 abstract 声明抽象类：用于接口部分类的实现（派生类继承抽象类时，实现完成）。抽象类包含抽象方法，抽象方法可被派生类实现。</p><p>
抽象类规则：</p><ul><li>
1.不能创建抽象类的实例 </li><li>2.不能在抽象类外定义抽象方法 </li><li>3.不能把抽象类声明为sealed（类前带关键字sealed代表该类是密封类，不能被继承）</li></ul>
<p>
关键字virtual声明虚方法:用于方法在继承类中的实现（在不同的继承类中有不同的实现）。</p><p>
抽象类和虚方法共同实现动态多态性。</p>
<p>
注：继承类中的重写虚函数需要声明关键字 override，在方法参数传入中写（类名 形参名）例如 public void CallArea(Shape sh)，意思是传入一个 shape 类型的类。</p><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">yuri</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;yuri</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;246***6318@qq.com</p></div></span>6年前 (2017-03-21)</div></div></li><!-- #comment-## -->
<li class="comment odd alt thread-odd thread-alt depth-1" id="comment-10740"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;p</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;roz***ech@gmail.com</p></div><div id="runoobvote-id-10740" data-commid = "10740" class="upvotejs"><a class="upvote"></a> <span class="count">102</span></div></div><div class="comt-main" id="div-comment-10740"><h2>virtual 和 abstract
</h2>
<p>virtual和abstract都是用来修饰父类的，通过覆盖父类的定义，让子类重新定义。</em>

<ul><li>
1.virtual修饰的方法必须有实现（哪怕是仅仅添加一对大括号),而abstract修饰的方法一定不能实现。</li><li>
2.virtual可以被子类重写，而abstract必须被子类重写。</li><li>
3.如果类成员被abstract修饰，则该类前必须添加abstract，因为只有抽象类才可以有抽象方法。</li><li>
4.无法创建abstract类的实例，只能被继承无法实例化。</li></ul>


<h2>

重载和重写
</h2>
<p>重载(overload)是提供了一种机制, 相同函数名通过不同的返回值类型以及参数来表来区分的机制。</p>

<blockquote>
  <p>见：<strong><a href="#overload" rel="nofollow">函数重载</a></strong></p>
</blockquote>

<p>重写(override)是用于重写基类的虚方法,这样在派生类中提供一个新的方法。</p>

<blockquote>
  <p> 见：<strong><a href="#override" rel="nofollow">动态多态性</a></strong></p>
</blockquote><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">p</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;p</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;roz***ech@gmail.com</p></div></span>6年前 (2017-04-06)</div></div></li><!-- #comment-## -->
<li class="comment even thread-even depth-1" id="comment-29313"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;zeng123m</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;705***981@qq.com</p><p><i class="fa fa-external-link" aria-hidden="true"></i> <a rel="nofollow" target="_blank" href="../w3cnote/what-is-a-virtual-method.html">&nbsp;&nbsp;参考地址</a></p></div><div id="runoobvote-id-29313" data-commid = "29313" class="upvotejs"><a class="upvote"></a> <span class="count">48</span></div></div><div class="comt-main" id="div-comment-29313"><p data-title="抽象方法和虚方法的区别" data-commid="10740"><strong>抽象方法和虚方法的区别</strong></p>
<ul><li>
1.虚方法必须有实现部分，抽象方法没有提供实现部分，抽象方法是一种强制派生类覆盖的方法，否则派生类将不能被实例化。
</li><li>
2.抽象方法只能在抽象类中声明，虚方法不是。如果类包含抽象方法，那么该类也是抽象的，也必须声明类是抽象的。
</li><li>
3.抽象方法必须在派生类中重写，这一点和接口类似，虚方法不需要再派生类中重写。
</li></ul>
<p>简单说，抽象方法是需要子类去实现的。虚方法是已经实现了的，可以被子类覆盖，也可以不覆盖，取决于需求。</p>

<p>抽象方法和虚方法都可以供派生类重写。</p><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="../note/29313">zeng123m</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;zeng123m</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;705***981@qq.com</p><p><i class="fa fa-external-link" aria-hidden="true"></i> <a rel="nofollow" target="_blank" href="../w3cnote/what-is-a-virtual-method.html">&nbsp;&nbsp;参考地址</a></p></div></span>5年前 (2018-07-09)</div></div></li><!-- #comment-## -->
<li class="comment odd alt thread-odd thread-alt depth-1" id="comment-29768"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;Lost丶先生</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;102***8263@qq.com</p><p><i class="fa fa-external-link" aria-hidden="true"></i> <a rel="nofollow" target="_blank" href="../w3cnote/csharp-polymorphism2.html">&nbsp;&nbsp;参考地址</a></p></div><div id="runoobvote-id-29768" data-commid = "29768" class="upvotejs"><a class="upvote"></a> <span class="count">93</span></div></div><div class="comt-main" id="div-comment-29768"><p>1、<strong>重载(overload)</strong>: 在同一个作用域(一般指一个类)的两个或多个方法函数名相同，参数列表不同的方法叫做重载，它们有三个特点(俗称两必须一可以):</p>
<ul><li>
方法名必须相同</li><li>
参数列表必须不相同</li><li>
返回值类型可以不相同</li></ul>
<p>例如：</p>
<pre>public void Sleep()
{
    Console.WriteLine("Animal睡觉");
}
public int Sleep(int time)
{
    Console.WriteLine("Animal{0}点睡觉", time);
    return time;
}</pre>
<p>
2、<strong>重写(override)</strong>:子类中为满足自己的需要来重复定义某个方法的不同实现，需要用 override 关键字，被重写的方法必须是虚方法，用的是 virtual 关键字。它的特点是(三个相同):</p>

<ul>
<li>相同的方法名</li>
<li>相同的参数列表</li>
<li>相同的返回值</li>
</ul>
<p>如：父类中的定义：</p>
<pre>public virtual void EatFood()
{
    Console.WriteLine("Animal吃东西");
}</pre>

<p>子类中的定义：</p>

<pre>public override void EatFood()
{
    Console.WriteLine("Cat吃东西");
    //base.EatFood();
}</pre>



<blockquote><p><strong>小提示：</strong>经常有童鞋问重载和重写的区别,而且网络上把这两个的区别作为 C# 做常考的面试题之一。实际上这两个概念完全没有关系，仅仅都带有一个“重”字。他们没有在一起比较的意义，仅仅分辨它们不同的定义就好了。</p></blockquote>
<p>3、<strong>虚方法</strong>：即为基类中定义的允许在派生类中重写的方法，使用virtual关键字定义。如：</p>
<pre>public virtual void EatFood()
{
    Console.WriteLine("Animal吃东西");
}</pre>


<p><strong>注意</strong>：虚方法也可以被直接调用。如：</p>
<pre>Animal a = new Animal();
a.EatFood();</pre>
<p>
执行输出结果为：</p>
<pre>Animal吃东西</pre>
<p> 4、<strong>抽象方法</strong>：在基类中定义的并且必须在派生类中重写的方法，使用 <span class="marked">abstract</span> 关键字定义。如：</p>
<pre>public abstract class Biology
{
    public abstract void Live();
}
public class Animal : Biology
{
    public override void Live()
    {
        Console.WriteLine("Animal重写的抽象方法");
        //throw new NotImplementedException();
    } 
}</pre>

<p><strong>注意：</strong>抽象方法只能在抽象类中定义，如果不在抽象类中定义，则会报出如下错误：</p>
<p><img src="//www.runoob.com/wp-content/uploads/2018/07/20171050-7907c8d2136643738cdc84b2f517d7f4.png"></p>


<blockquote><p><strong>虚方法和抽象方法的区别是</strong>：因为抽象类无法实例化，所以抽象方法没有办法被调用，也就是说抽象方法永远不可能被实现。</p></blockquote>
 <p>5、<strong>隐藏方法</strong>：在派生类中定义的和基类中的某个方法同名的方法，使用 new 关键字定义。如在基类 Animal 中有一方法 Sleep():</p>
<pre>public void Sleep()
{
    Console.WriteLine("Animal Sleep");
}</pre>


<p>则在派生类 Cat 中定义隐藏方法的代码为：</p>
<pre>new public void Sleep()
{
    Console.WriteLine("Cat Sleep");
}</pre>


<p>或者为：</p>
<pre>public new void Sleep()
{
    Console.WriteLine("Cat Sleep");
} </pre>   
<p><strong>注意：</strong></p><ul><li>（1）隐藏方法不但可以隐藏基类中的虚方法，而且也可以隐藏基类中的非虚方法。
</li><li>（2）隐藏方法中父类的实例调用父类的方法，子类的实例调用子类的方法。
</li><li>（3）和上一条对比：重写方法中子类的变量调用子类重写的方法，父类的变量要看这个父类引用的是子类的实例还是本身的实例，如果引用的是父类的实例那么调用基类的方法，如果引用的是派生类的实例则调用派生类的方法。</li></ul>


<blockquote><p><strong>更多内容可参考： <a href="../w3cnote/csharp-polymorphism2.html" target="_blank" rel="noopener nofollow">C# 中的多态性</a></strong></p></blockquote>

<div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">Lost丶先生</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;Lost丶先生</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;102***8263@qq.com</p><p><i class="fa fa-external-link" aria-hidden="true"></i> <a rel="nofollow" target="_blank" href="../w3cnote/csharp-polymorphism2.html">&nbsp;&nbsp;参考地址</a></p></div></span>5年前 (2018-07-18)</div></div></li><!-- #comment-## -->
<li class="comment even thread-even depth-1" id="comment-30595"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;Marco</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;329***308@qq.com</p></div><div id="runoobvote-id-30595" data-commid = "30595" class="upvotejs"><a class="upvote"></a> <span class="count">52</span></div></div><div class="comt-main" id="div-comment-30595"><p><strong>虚方法的调用：</strong>调用上，使用子类构造的对象调用虚方法，就会调用子类的方法，使用父类构造的对象，就会调用父类的方法。</p>

<p><strong>
隐藏方法的调用：</strong>调用上， 使用子类类型的声明调用隐藏方法，就会调用到子类的方法。若想调用被隐藏的方法，需要用父类类型的声明来调用。</p>
<p>调用不同的举例:</p>

<pre>class Enemy
{
    public void Move() {
        Console.WriteLine("调用了 enemy的move方法");
    }
    public virtual void Attack() {
        Console.WriteLine("enemy attac");
    }
    }


    class Boss : Enemy
    {
    public override void Attack() {
        Console.WriteLine("Boss Attac");
    }

    public new void Move() {
        Console.WriteLine("Boss move");
    }
}

static void Main(string[] args)
{
    //---- 隐藏方法的调用----begin
    Boss oneEnemy = new Boss();
    oneEnemy.Move(); // 调用的是隐藏方法， 用子类的声明来调用的，调用的就是子类的Move。

    Enemy twoEnemy = new Boss();
    twoEnemy.Move(); // 调用的隐藏方法， 用父类的声明来调用的，调用的就是父类的Move方法。
    //-----------------------end

    //-----虚方法的调用----- begin
    用什么类型 来构造，在调用方法的时候就会调用什么类型的方法。

    Enemy threeEnemy = new Enemy();
    threeEnemy.Attac(); // 调用虚方法，用父类来实例化的，所以调用的是父类的Attac方法。

    Enemy fourEnemy = new Boss();
    fourEnemy.Attac();  // 调用虚方法，用子类来实例化的，所以调用的就是子类(Boss)的Attac方法。

    //-----虚方法的调用------end

    Console.ReadKey();
}</pre><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">Marco</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;Marco</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;329***308@qq.com</p></div></span>5年前 (2018-07-28)</div></div></li><!-- #comment-## -->
<li class="comment odd alt thread-odd thread-alt depth-1" id="comment-34641"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;lanya13</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;har***323@126.com</p></div><div id="runoobvote-id-34641" data-commid = "34641" class="upvotejs"><a class="upvote"></a> <span class="count">9</span></div></div><div class="comt-main" id="div-comment-34641"><p>原文中抽象类的例子其实没有体现多态性，可以再加一个继承类（三角形面积），以体现多态。</p>

<pre>using System;
namespace PolymorphismApplication
{
    abstract class Shape
    {
        public abstract int area();
    }
    
    class Rectangle : Shape
    {
        private int length;
        private int width;
        public Rectangle(int a = 0, int b = 0)
        {
            length = a;
            width = b;
        }
        public override int area()
        {
            //Console.WriteLine("Rectangle 类的面积：");
            return (width * length);
        }
    }

    class triangle : Shape
    {
        private int baseLine;
        private int height;
        public triangle(int a = 0, int b = 0)
        {
            baseLine = a;
            height = b;
        }
        public override int area()
        {
            //Console.WriteLine("三角形类的面积：");
            return (2 *baseLine* height/4);
        }
    }

    class RectangleTester
    {
        static void Main(string[] args)
        {
            Rectangle r = new Rectangle(10, 7);
            double a = r.area();
            triangle t = new triangle(10, 7);
            double b = t.area();
            Console.WriteLine("长方形面积： {0}, 三角形面积：{1}", a, b);
            Console.ReadKey();
        }
    }
}</pre><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">lanya13</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;lanya13</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;har***323@126.com</p></div></span>5年前 (2018-08-31)</div></div></li><!-- #comment-## -->
<li class="comment even thread-even depth-1" id="comment-42919"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;维乐紫刃</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;vrb***lor@126.com</p></div><div id="runoobvote-id-42919" data-commid = "42919" class="upvotejs"><a class="upvote"></a> <span class="count">47</span></div></div><div class="comt-main" id="div-comment-42919"><p>自己写了个继承，分别写了隐藏方法跟重写方法，生成三个实例来演示一下。</p>

<pre>namespace MySpace
{
    class dad
    {
        protected string name;
        public dad(string n)
        {
            name = n;
        }
        public void say()
        {
            Console.WriteLine("I am {0}.", name);
        }
        public virtual void growup()
        {
            Console.WriteLine("{0} has grown old.", name);
        }
    }
    class son:dad
    {
        public son(string n) : base(n)
        {
            //name = n;
        }
        public new void say()
        {
            Console.WriteLine("I am {0} and a son.",name);
        }
        public override void growup()
        {
            //base.growup();
            Console.WriteLine("{0} is growing up.",name);
        }
    }
    class entrance
    {
        public static void Main()
        {
            dad grandpa = new dad("grandpa");
            grandpa.say();
            grandpa.growup();
            dad father = new son("father");
            father.say();
            father.growup();
            son tom = new son("Tom");
            tom.say();
            tom.growup();
            Console.ReadKey();
        }
    }
}</pre>

<p>运行结果为：</p>
<pre>I am grandpa.
grandpa has grown old.
I am father.
father is growing up.
I am Tom and a son.
Tom is growing up.</pre>

<p>上边的结果：</p>
<ul><li>
1）用父类生成的父类对象，grandpa，访问隐藏方法是父类的方法，访问重写方法是父类的方法
</li><li>
2）用子类生成的父类对象，father，访问隐藏方法是父类的方法，访问重写方法是子类的方法
</li><li>
3）用子类生成的子类对象，son，访问隐藏方法是子类的方法，访问重写方法是子类的方法
</li></ul>
<div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">维乐紫刃</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;维乐紫刃</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;vrb***lor@126.com</p></div></span>4年前 (2019-05-20)</div></div></li><!-- #comment-## -->
<li class="comment odd alt thread-odd thread-alt depth-1" id="comment-54994"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;谷岳添</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;hoo***ni@qq.com</p></div><div id="runoobvote-id-54994" data-commid = "54994" class="upvotejs"><a class="upvote"></a> <span class="count">26</span></div></div><div class="comt-main" id="div-comment-54994"><p>这才是真的多态：</p>

<pre>using System;

class Animal
{ 
    public virtual void Eat()
    {
        Console.WriteLine("这是animal的eat方法");
    }
}

class Dog:Animal
{
    public override void Eat()
    {
        Console.WriteLine("这是dog的eat");
    }
}

class Cat : Animal
{
    public override void Eat()
    {
        Console.WriteLine("这是cat的eat");
    }

}
class Program
{

    static void Main(string[] args) 
    {
        // 多态的实现前提是继承和方法重写，基类可以new所有的派生类 new哪个类，他就执行那个类的方法
        Animal animal1 = new Animal(); // 实例Animal类
        Animal animal2 = new Dog(); // 实例Dog类
        Animal animal3 = new Cat(); // 实例Cat类

        animal1.Eat(); // 调用Animal类的eat方法
        animal2.Eat(); // 实例Dog类
        animal3.Eat(); // 实例Cat类
    }

}</pre><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">谷岳添</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;谷岳添</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;hoo***ni@qq.com</p></div></span>3年前 (2020-07-03)</div></div></li><!-- #comment-## -->
<li class="comment even thread-even depth-1" id="comment-68377"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;大聪明学府</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;253***6969@qq.com</p></div><div id="runoobvote-id-68377" data-commid = "68377" class="upvotejs"><a class="upvote"></a> <span class="count">5</span></div></div><div class="comt-main" id="div-comment-68377"><p>函数重载简单实例：</p>

<pre>using System;

namespace Emmmm
{
    public class Discern
    {
        public static void DiscernTypeof(int a)
        {
            Console.WriteLine("{0} is int.", a);
        }
        public static void DiscernTypeof(string a)
        {
            Console.WriteLine("\"{0}\" is string.", a);
        }
        public static void DiscernTypeof(char a)
        {
            Console.WriteLine("{0} is char.", a);
        }
        public static void DiscernTypeof(float a)
        {
            Console.WriteLine("{0} is float.", a);
        }
        public static void DiscernTypeof(double a)
        {
            Console.WriteLine("{0} is double.", a);
        }
        public static void DiscernTypeof(bool a)
        {
            Console.WriteLine("{0} is boolean.", a);
        }
        public static void DiscernTypeof(long a)
        {
            Console.WriteLine("{0} is long.", a);
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            Discern.DiscernTypeof(233);
            Discern.DiscernTypeof("aaa");
            Discern.DiscernTypeof('c');
            Discern.DiscernTypeof(233.233F);
            Discern.DiscernTypeof(23456277824367496L);
            Discern.DiscernTypeof(233.43285679368574D);
            Discern.DiscernTypeof(false);
        }
    }
}</pre>
<p>结果：</p>

<pre>233 is int.
"aaa" is string.
c is char.
233.233 is float.
23456277824367496 is long.
233.43285679368574 is double.
False is boolean.</pre><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">大聪明学府</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;大聪明学府</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;253***6969@qq.com</p></div></span>1年前 (2021-11-21)</div></div></li><!-- #comment-## -->
<li class="comment odd alt thread-odd thread-alt depth-1" id="comment-77833"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;苏</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;sus***09643@outlook.com</p><p><i class="fa fa-external-link" aria-hidden="true"></i> <a rel="nofollow" target="_blank" href="http://chat.openai.com">&nbsp;&nbsp;参考地址</a></p></div><div id="runoobvote-id-77833" data-commid = "77833" class="upvotejs"><a class="upvote"></a> <span class="count">3</span></div></div><div class="comt-main" id="div-comment-77833"><p>抽象类和抽象方法以及虚方法都是面向对象编程中的重要概念，用于实现多态性和继承。</p><p>抽象类和抽象方法适用于以下场景：</p><ul><li>当需要定义一个类，但是这个类的具体实现是由子类来完成时，可以定义一个抽象类，并在抽象类中定义抽象方法。这样，在子类中必须实现这些抽象方法，以完成具体的实现。</li><li>当需要约束一些子类必须实现某些方法时，可以使用抽象类和抽象方法。</li></ul><p>虚方法适用于以下场景：</p><ul><li>当需要在基类中提供一个默认实现，但是子类可以选择覆盖这个实现时，可以使用虚方法。这样，在子类中可以使用 <code>override</code> 关键字覆盖基类中的虚方法，从而实现自己的逻辑。</li></ul><p>总的来说，抽象类和抽象方法更适合用于约束和规范类的继承结构和方法的实现，而虚方法则更适合用于提供默认实现和让子类进行覆盖的场景。</p><p></p><p>在抽象类中，除了抽象方法，也可以声明以下成员为抽象成员：</p><ol><li><p>抽象属性（abstract properties）：类似于抽象方法，没有实现体，只有声明，需要在具体的子类中实现。</p></li><li><p>抽象事件（abstract events）：类似于抽象方法和属性，需要在具体的子类中实现。</p></li><li><p>抽象索引器（abstract indexers）：类似于抽象属性，没有实现体，只有声明，需要在具体的子类中实现。</p></li></ol><p></p><p></p><p>除了虚方法之外，类中还可以有以下虚成员：</p><ol><li><p>虚属性（Virtual Properties）：使用<code>virtual</code>关键字定义的属性，可以在子类中重写。</p></li><li><p>虚索引器（Virtual Indexers）：使用<code>virtual</code>关键字定义的索引器，可以在子类中重写。</p></li><li><p>虚事件（Virtual Events）：使用<code>virtual</code>关键字定义的事件，可以在子类中重写。</p></li></ol><p>虚成员的作用和虚方法类似，可以在派生类中进行重写以满足不同的需求。同时，虚成员也可以提高代码的可重用性和可扩展性。</p><p></p><p>——ChatGPT</p><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">苏</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;苏</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;sus***09643@outlook.com</p><p><i class="fa fa-external-link" aria-hidden="true"></i> <a rel="nofollow" target="_blank" href="http://chat.openai.com">&nbsp;&nbsp;参考地址</a></p></div></span>2个月前 (02-27)</div></div></li><!-- #comment-## -->
	</ol>
	<div class="pagenav">
			</div>
</div>
<div id="respond" class="no_webshot"> 
		<div class="comment-signarea" style="display:none; padding: 20px 20px;"> 
	<h3 class="text-muted" id="share_code" style="color: #799961;"><i class="fa fa-pencil-square-o" aria-hidden="true"></i> 点我分享笔记</h3>
	<!--
	<p style="font-size:14px;">笔记需要是本篇文章的内容扩展！</p><br>
	<p style="font-size:12px;"><a href="../tougao" target="_blank">文章投稿，可点击这里</a></p>
	<p style="font-size:14px;"><a href="../w3cnote/runoob-user-test-intro.html#invite" target="_blank">注册邀请码获取方式</a></p>
		<h3 class="text-muted"><i class="fa fa-info-circle" aria-hidden="true"></i> 分享笔记前必须<a href="javascript:;" class="runoob-pop">登录</a>！</h3>
		<p><a href="../w3cnote/runoob-user-test-intro.html#invite" target="_blank">注册邀请码获取方式</a></p>-->
	</div>
		
	<form action="/wp-content/themes/runoob/option/addnote.php" method="post" id="commentform" style="display:none;">
		<div class="comt">
			<div class="comt-title">
				<i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i>				<p><a id="cancel-comment-reply-link" href="javascript:;">取消</a></p>
			</div>
			<div class="comt-box">
			<div id="mded"></div>
			
				<div class="comt-ctrl">
					<div class="comt-tips"><input type='hidden' name='comment_post_ID' value='6643' id='comment_post_ID' />
<input type='hidden' name='comment_parent' id='comment_parent' value='0' />
</div>
					<button type="submit" name="submit" id="submit" tabindex="5"><i class="fa fa-pencil" aria-hidden="true"></i> 分享笔记</button>
				</div>
			</div>
		
				
					<div class="comt-comterinfo"> 
						<ul id="comment-author-info">
							<li class="form-inline"><label class="hide" for="author">昵称</label><input class="ipt" type="text" name="author" id="author" value="" tabindex="2" placeholder="昵称"><span class="text-muted">昵称 (必填)</span></li>
							<li class="form-inline"><label class="hide" for="email">邮箱</label><input class="ipt" type="text" name="email" id="email" value="" tabindex="3" placeholder="邮箱"><span class="text-muted">邮箱 (必填)</span></li>
							<li class="form-inline"><label class="hide" for="url">引用地址</label><input class="ipt" type="text" name="url" id="url" value="" tabindex="4" placeholder="引用地址"><span class="text-muted">引用地址</span></li>
						</ul>
					</div>
				
			
		</div>

	</form>
	</div>
<script type="text/javascript">
$(function() {
	//初始化编辑器
	
	var editor = new Simditor({
	  textarea: $('#mded'),
	  placeholder: '写笔记...',
	  upload:false,
	 // upload: {url:'/api/comment_upload_file.php',params: null,fileKey: 'upload_file',connectionCount: 1,leaveConfirm: '文件正在上传，您确定离开?'},
	  defaultImage: 'https://www.runoob.com/images/logo.png',
	  codeLanguages: '',
	  autosave: 'editor-content',
	  toolbar: [  'bold','code','ul','ol','image' ]
	});
	editor.on('selectionchanged', function() {
		$(".code-popover").hide();
	});

	// 提交数据
	$("#share_code").click(function() {
		$(".comment-signarea").hide();
		$("#commentform").show();
		
	});
	$("#user_add_note").click(function() {
		$(".comment-signarea").hide();
		$("#commentform").show();
		$('html, body').animate({
       	    scrollTop: $("#respond").offset().top
    	}, 200);
	});

	// 提交笔记
	var commentform=$('#commentform');
	commentform.prepend('<div id="comment-status" style="display:none;" ></div>');
	var statusdiv=$('#comment-status');
	
	commentform.submit(function(e){
		e.preventDefault();
		var noteContent = editor.getValue();
		// console.log(noteContent);
		noteContent = noteContent.replace(/<pre><code>/g,"<pre>");
		noteContent = noteContent.replace(/<\/code><\/pre>/g,"</pre>");
		
		// 系列化表单数据
		var comment_parent = 0;
		var is_user_logged_in = $("#is_user_logged_in").val();
		var comment_post_ID =  6643;
		var _wp_unfiltered_html_comment = $("#_wp_unfiltered_html_comment").val();
		var comment = noteContent;
		var author = $("#author").val();
		var url = $("#url").val();
		var email = $("#email").val();
		if(isBlank(author) && is_user_logged_in==0) {
			statusdiv.html('<p  class="ajax-error">请输入昵称！</p>').show();
		} else if(isBlank(email)  && is_user_logged_in==0) {
			statusdiv.html('<p  class="ajax-error">请输入邮箱！</p>').show();
		} else {
			// var formdata=commentform.serialize() + "&comment=" + noteContent ;
			// 添加状态信息
			statusdiv.html('<p>Processing...</p>').show();
			// 获取表单提交地址
			var formurl=commentform.attr('action');
			
			// 异步提交
			$.ajax({
					type: 'post',
					url: formurl,
					dataType:'json',
					data: {"comment_parent":comment_parent,"comment_post_ID":comment_post_ID, "_wp_unfiltered_html_comment":_wp_unfiltered_html_comment,"comment":comment,"url":url, "email":email,"author":author},
					error: function(XMLHttpRequest, textStatus, errorThrown){
					statusdiv.html('<p class="ajax-error" >数据不完整或表单提交太快了！</p>').show();
				},
				success: function(data, textStatus){
					if(data.errorno=="0") {
						$("#submit").prop('disabled', true);
						statusdiv.html('<p class="ajax-success" >笔记已提交审核，感谢分享笔记！</p>').show();
						alert('笔记已提交审核，感谢分享笔记！');
					}else{
						statusdiv.html('<p class="ajax-error" >'+data.msg+'</p>').show();
					}
					commentform.find('textarea[name=comment]').val('');
				}
			});
			setTimeout(function(){
		        $("#submit").prop('disabled', false);
		    }, 10*1000);
		}
		return false;

	});
	$(".comt-author").click(function() {
		href = $(this).children("a").attr("href");
		if(href.indexOf("/note/")!=-1) {
			var win = window.open(href, '_blank');
  			win.focus();
		}
	});
	$(".comt-meta span").hover(function(){
		$(this).children(".tooltip").css({ "opacity": 1, "pointer-events": "auto"});
	},function(){
		$(this).children(".tooltip").removeAttr("style");
	});
	/*
	$(".wrapper i").hover(function(){
		$(this).siblings(".tooltip").css({ "opacity": 1, "pointer-events": "auto"});
	},function(){
		$(this).siblings(".tooltip").css({ "opacity": 0, "pointer-events": "auto"});
	});
	*/
	//Upvote.create('runoobvote-id', {callback: vote_callback});
	var ajaxurl = 'https://www.runoob.com/wp-admin/admin-ajax.php';
	var callback = function(data) {
		//console.log($('#runoobvote-id').upvote('upvoted'));
		//console.log($('#runoobvote-id').upvote('downvoted'));
		//console.log(data);
		_vote_action = data.action;
		id_arr = data.id.split('-');
		um_id= id_arr[2];
		//console.log(um_id);
		
		var re = /^[1-9]+/;
		if (re.test(um_id)) { 
			var ajax_data = {
				_vote_action: _vote_action,
				action: "pinglun_zan",
				um_id: um_id,
				um_action: "ding"
			};
			//console.log(ajax_data);
			$.post(ajaxurl,ajax_data,function(status){
				//if(status.vote_num>999) {
				//	_voteHtml = '<span style="display: block; text-align: center;font-size: 20px; color: #6a737c; margin: 8px 0;">'+kFormatter(status.vote_num) +'</span>';
				//	$("#runoobvote-id-" + um_id + " .count").hide().after(_voteHtml);
				//}
				
			});
		}
	};
	if($('#comments').length && $('.upvotejs').length){
		$('.upvotejs').upvote({id: 6643, callback: callback});
	
		$.post(ajaxurl,{"action":"pinglun_zan","postid":6643},function(data){  
			$(data).each(function(key,value) {
				$("#runoobvote-id-" + value.commid + " .upvote").addClass(value.upvotejs_class);
				$("#runoobvote-id-" + value.commid + " .downvote").addClass(value.downvote_class);
				$("#runoobvote-id-" + value.commid + " .count").text(value.upvote_count);
			})
		},'json');
		
	}
	
	
});
function isBlank(str) {
    return (!str || /^\s*$/.test(str));
}
function kFormatter(num) {
	// return num;
    return Math.abs(num) > 999 ? Math.sign(num)*((Math.abs(num)/1000).toFixed(1)) + 'k' : Math.sign(num)*Math.abs(num)
}

</script>

<link rel="stylesheet" href="../0/qa.css?1.44">
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